Changes of Soil Aggregate Stability and Erodibility After Cropland Conversion in Degraded Karst Region

Cropland (CL) conversion can be an effective strategy to restore soil functions, enhance soil aggregate stability, and control soil erosion. A multitude of soil properties have been suggested to contribute to aggregate stability, but the key soil factors are rarely evaluated in degraded karst regions. This study aimed to evaluate the effects of CL conversion strategies on soil aggregate stability and erodibility and identify key effective factors in degraded karst region. We selected two CL conversion strategies, namely conversions with natural secondary forest (SF) and Chinese prickly ash (CP, artificial forest) and used CL as a reference. Distribution of aggregates, mean weight diameter (MWD), geometric mean diameter (GMD), soil erodibility (K value), and soil properties such as soil organic carbon (SOC), easily oxidizable organic carbon (EOC), particulate organic carbon (POC), nitrogen (N), bacterial quantity (Bq), bulk density (BD), soil water (SW), and exchangeable Ca were measured at a depth of 0–10 cm. SF and CP demonstrated a significantly higher proportion of large macroaggregates (> 2 mm), MWD, and GMD but a significantly lower proportion of aggregates with a size of < 2 mm and K values than CL. The changes of soil aggregate fractions and stability and erodibility were strongly related to SOC, POC, EOC, N, SW, Bq, and BD. Classification and regression tree analysis further revealed that EOC demonstrated the maximum effects on MWD and K values. This study indicated that CL conversions can promote large macroaggregate formation, improve aggregate stability, and decrease the risk of soil erosion through their impacts on soil properties. EOC showed the strongest effects on soil aggregate stability and soil erodibility. The natural SF can demonstrate better improvement on the stability of aggregate and soil anti-erosion capability than artificial forest (CP).